Throughout this application various publications are referenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed in this application.
Glutamate receptors are believed to be the principal excitatory neurotransmitter receptors in the central nervous system (CNS). Based on the chemicals that activate glutamate receptors, such receptors are generally divided into three major subtypes: quisqualate (QUIS-R), N-methyl-D-aspartate (NMDA-R), and kainate (KAIN-R). These receptors are involved in development, learning and neuropathology and likely mediate the neurodegenerative consequences of hypoxemia, epilepsy, Alzheimer's disease, and Huntington's disease (1-5). There is considerable interest in developing agents that block glutamate receptors, particularly antagonists of the NMDA type receptor because of their anticonvulsant action and possible protection from ischemic brain damage (7). NMDA receptors are involved in a variety of neurological and psychiatric disorders, and antagonists of this receptor may be therapeutically valuable in movement disorders, such as epilepsy, and in various acute and chronic neurodegenerative disorders.
Studies of glutamate receptors, in particular studies employing biochemical techniques, have been made difficult by the relative paucity of potent antagonists for these receptor proteins. Selective, competitive and non-competitive antagonists of the NMDA receptor have become available during the past few years, but the search for antagonists of the L-quisqualate-sensitive receptor has only recently shown signs of success (8-10). Quisqualate-sensitive glutamate receptors are distributed widely in excitable tissues of multicellular animals (11) and studies of the effects of the venoms of certain wasps and spiders on vertebrate and invertebrate neurons and muscle fibers suggest that one source of antagonists for this class of receptor might be the venoms of some species of predaceous arthropods (12-17).
The solitary digger wasp Philanthus triangulum F., which is a sphecid wasp that preys on honey bees, manufactures a venom which blocks glutamate receptors on locust skeletal muscle (16,17). Piek and colleagues have shown that the venom of this wasp contains a component (termed .delta.-philanthotoxin) which exhibits a number of pharmacological properties including open channel block of junctional glutamate receptors (18) and extrajunctional glutamate D-receptors (19) of locust leg muscle, most of which are quisqualate-sensitive (20). However, Piek and colleagues did not isolate or determine the active compound of the venom component.
In order to deduct the active ingredient contained in venom from the wasp Philanthus triangulum F., a series of extractions were performed to isolate an active fraction. Based on a structure deduced from chemical analysis of the fraction, a series of related compounds were synthesized and their activities and chemical properties compared to those of the venom extract fraction. This resulted in the unexpected discovery of the active compound of the venom. The present invention concerns the active ingredient contained in venom from the wasp Philanthus triangulum F., the chemical structure of this active ingredient, a method for synthesizing the ingredient, designated philanthotoxin-433 PhTX-433, and the use of PhTX-433 as a potent inhibitor of the glutamate receptors. In addition, the present invention involves the synthesis of pharmacologically active analogs of this ingredient, e.g., PhTX-334, PhTX-343 and many others (wherein the numerals denote the number of methylenes between the amino groups of the spermine moiety).